public class Solution41 {
    public int firstMissingPositive(int[] nums) {
        int n = nums.length;
        for (int i = 0; i < n; i++) {
            while((nums[i] > 0 && nums[i] < n) &&
                    nums[nums[i] - 1] != nums[i]){
                int temp = nums[i];
                nums[i] = nums[nums[i] - 1];
                nums[nums[i] - 1] = temp;
            }
        }
        for(int i = 0;i < n;i++){
            if(nums[i] != i+1){
                return i + 1;
            }
        }
        return n + 1;
    }
}
